Modern telephones allow for the connection of a multitude of devices ranging from traditional wired, analog telephones to cordless telephones and digital cellular phones and even Internet connected audio communication devices. The deregulation of the telephone companies has resulted in a general relaxation of the performance specifications and interface specifications. In fact, customers have disadvantageously accepted a significant degradation in the sound quality of telephone communications in exchange for convenience and mobility. This has made the task of designing a telephone headset adapter that gives the best perceived sound quality in all situations exceedingly difficult. What sounds most natural and clear in a quiet environment using traditional wired telephones does not provide the most intelligible speech when the far-end caller is in a fast moving car on a cellphone. Similarly, an adapter design that is optimized to provide the most effective communication in a noisy office will perform poorly in a competitive comparison with a simple, linear headset amplifier in a quiet, acoustically treated room.
Traditionally, telephone headset adapter systems were designed to perform well in noisy and/or distorted conditions. The audio bandwidth was limited to only those frequencies essential for speech, and non-linear processing techniques, such as gain switching or expansions, were used to provide some degree of background noise cancellation. However, as the competitive landscape expands, customers have more choices of products, and with the sound quality improvement of digital communications, they are choosing products that provide more natural sounds. Most headset users are unaware of the intelligibility benefits of bandwidth limiting and non-linear processing in adverse environments and rather see these attributes as negative. When confronted with a poor quality call, the user typically only has access to a volume control and, therefore, has to increase the loudness and/or ask callers to repeat themselves until the user can understand a caller. For a call center company, a poor quality call may result in lost revenue for the company because the call center agent may be required to ask the caller to repeat himself or herself. This resulting delay can prevent the call center agent from accepting calls from other callers, and this can negatively impact the revenue stream of the company.
Recent adapter systems have provided a tone control to allow the user to adjust the tonal quality of the sound. While this allows the user to “tune” the sound to the caller's voice and the user's personal preference, this feature does little to improve intelligibility by improving the signal to noise ratio. This feature is more like a selective loudness control, by making some part of the speech spectrum louder in an attempt to permit the user to understand the caller.
Some current voice expander circuits are useful in improving the signal to noise ratio, but their performance is increasingly compromised by the relaxing telephony standards which give rise to greatly varying signal levels and spectra depending on the source of the call. The expander threshold for these circuits can not be set to a fixed level for all types of call.
Therefore, the current technologies are limited to particular capabilities and suffer from various constraints.